5

Lots of reasons:
At your age perimenopause is the most likely answer. Pregnancy, stress, dysfunctional uterine bleeding, annovulatory cycles and many other things are also possible. If you are concerned, it is time to call your family doctor! until you know for sure, just to be safe, don't to anything that would hurt your baby if you are pregnant.
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6

Sex:
if your talking about the whole process, one will achieve orgasm. A pleasureful sensation, relaxation of the mind, and to be intuned with your body on a newer level. Your skin is more sensitive to touch, and senses more hightened.
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8

No:
"sex headaches" are more common in men, often just before or during orgasm. Usually these don't indicate anything worrisome. But if it comes on suddenly rather than building gradually, and it's your first one, it's best to see a doctor (primary care physician or neurologist, etc) for an evaluation. More info for you here: http://www.Mayoclinic.Com/health/sex-headaches/ds00645.
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